Adsorption of ammonium from simulated wastewater by montmorillonite nanoclay and natural vermiculite: experimental study and simulation.

Abstract

In this research, montmorillonite nanoclay (MNC) and vermiculite were used to adsorb ammonium (NH4+) from simulated wastewater. The effect of organic acids, cations, and anions on adsorption of NH4+ was also studied using batch experiments. The presence of organic acids significantly decreased the NH4+ adsorption using both adsorbents and the reduction followed the order of citric acid>malic acid>oxalic acid. The presence of cations in wastewater could decrease the adsorption of NH4+ and the ion exchange selectivity on the MNC and vermiculite followed the orders Mg>Ca≥K>Na and Mg >>Ca>Na>K, respectively. Adsorption of NH4+ by adsorbents in the presence of sulfate (SO4) was higher than those in the presence of phosphate (PO4) and chloride (Cl) anions. Results indicated that MNC and vermiculite had good potential for NH4+ removal depending on adsorbent dosage, pH, contact time, and initial NH4+ concentration. The effect of pH on removal of NH4+ indicated that MNC would be more appropriate as the adsorbent than vermiculite at low pH values. Kinetic analysis demonstrated that the rate-controlling step adsorption for NH4+ by MNC and vermiculite was heterogeneous chemisorption and followed the pseudo-second-order model. The desorption experiments indicated that the adsorption of NH4+ by adsorbents was not fully reversible, and the total recovery of adsorbed NH4+ for MNC and vermiculite varied in the range of 72 to 94.6% and 11.5 to 45.7%, respectively. Cation exchange model (CEM) in PHREEQC program was used to simulate NH4+ adsorption. Agreement between measured and simulated data suggested that CEM was favored in simulating adsorption of NH4+ by clay minerals. The results indicated that MNC and vermiculite have good performance as economic and nature-friendly adsorbents that can ameliorate the water and environment quality.